The invention relates to a method for non-releasable fixing of at least one component to a further component and to hot rivet joints.
German Patent Document No. DE 10 2006 028 771 A2 discloses a hot rivet joint and a method for production thereof. During hot riveting a hot rivet is introduced into an opening of a component and welded via an end face of a shank of the hot rivet to a surface of a further component. This can be achieved through resistance welding, in particular through projection welding. The shank of the hot rivet is then heat compressed, with plastic deformation of the hot rivet, until a head of the hot rivet lies at least in areas on a surface of the first component. During compression, material of the shank is laterally displaced and fills at least some areas of the opening of the first component. A pre-stressing force that fixes the components against each other is produced between the two components.
The pre-stressing force cannot be adjusted, however, in known hot riveting methods. In association with additional operating forces, however, excessive pre-stressing force can lead to overloading and failure of the hot rivet joint.
Accordingly, exemplary embodiments of the present invention are directed to a method and a hot rivet joint in which a predefined pre-stressing force can be adjusted between the components to be joined.
In a method for non-releasable fixing of at least one component to a further component a hot rivet is introduced into an opening of the at least one first component and an end face of a shank of the hot rivet is welded to a surface of the further component. Subsequently, with plastic deformation of the hot rivet, the shank of the hot rivet is compressed until a head of the hot rivet lies with a pre-stressing force at least in areas on a surface of the at least one component.
According to exemplary embodiments of the present invention the pre-stressing force, with which the head of the hot rivet lies at least in areas on the surface of the at least one component, is adjusted to a predefined value. Thus, a hot rivet joint can be created that is designed so that the total of the pre-stressing force and loads of the hot rivet joint arising in operation always remains below a maximum force. A failure of the hot rivet joint under operating loads is thus reliably avoided.
In order to adjust the pre-stressing force suitable hot rivets are thereby selected according to the operating load to be expected. An essential factor here is the elasticity between the rivet head or the bearing of the rivet head and the shank of the hot rivet. In order to reduce the pre-stressing force, for example, a rivet with a recess in the form of a hollow channeling between the shank and the head can be selected. The selection of a hot rivet with suitable head thickness and/or a suitable leverage ratio between the shank and head bearing surface on the at least one component can serve for adjusting the pre-stressing force.
A further possibility for adjusting the pre-stressing force lies in the selection of a hot rivet with a suitably designed shank. For example, rivets with purposefully limited heat compressible areas can be selected. Such rivets have a geometric diameter graduation. Only the shank length portion with the smallest cross-section is compressed during the hot riveting. The contraction of the rivet shank during cooling is limited to the heated region, whereby the pre-stressing force thereby arising is then reduced.
The pre-stressing force can also be adjusted through the design of the receiving opening for the hot rivet. In this connection, for example, undercuts can be provided that act as purposefully selected elasticities.
A further possibility for selecting the pre-stressing force lies in the adjustment of the process parameters during welding or compression of the hot rivet. With increasing electrode force between an electrode used for welding or heat compression the compression takes place at a lower rivet shank temperature. Due to the low resulting contraction of the compressed rivet a lower pre-stressing force is achieved. The amount of heat applied during the hot riveting can also be used to adjust the pre-stressing force. By combining a rivet flow value and a riveting-in time the amount of heat can be controlled. Smaller amounts of heat lead to lower pre-stressing force, large amounts of heat to higher pre-stressing forces.
The invention further relates to a hot rivet joint for non-releasable fixing of at least one component to a further component. The hot rivet joint comprises a hot rivet with a head and a shank connecting thereto, of which the end face facing away from the head is welded to a surface of the further component, wherein the shank of the hot rivet is compressed under plastic deformation. According to exemplary embodiments of the invention, a recess is provided in the transition region between the head and the shank, by means of which a pre-stressing force for at least area-wise bearing of the head on a surface of the at least one component can be adjusted to a predefined value. Through such a recess, which can, for example, be in the form of peripheral channeling surrounding the connection region between the head and the shank, the elasticity of the hot rivet is increased so that the hot rivet joint all in all has a low pre-stressing force.
The further aspects of the invention described below can be used either independently or also in combination.
A further aspect of the invention relates to a hot rivet joint of the type described, in which according to the invention the thickness of the head of the hot rivet is designed for adjustment of a pre-stressing force for the at least area-wise bearing of the head on a surface of the at least one component to a predefined value. Hot rivets with a small head thickness hereby lead to a lower pre-stressing force, as also here the elasticity in the transition region between the head and shank of the hot rivet is increased.
An adjustment of the pre-stressing force to predefined values is also possible so that overloading of the rivet joint through the pre-stressing force in connection with the operating load is avoided.
In a further aspect of the invention a ratio of a bearing surface of the head on a surface of the at least one component to a cross-sectional area of the shank is provided by means of which a pre-stressing force for at least area-wise bearing of the head on a surface of the at least one component can be adjusted to a predefined value. This leverage ratio determines the rigidities of the rivet and therefore directly influences the pre-stressing force so that here also overloading is reliably avoided by selecting a suitable leverage ratio.
A further aspect of the invention relates to a hot rivet joint of the type described, in which according to the invention the shank of the hot rivet comprises a first and a second length region, whereby merely one of the two length regions of the shank is compressed under plastic deformation. This can be realised by selecting a hot rivet with two length regions of different cross-sections, whereby during compression of the hot rivet merely the region with the smaller cross-section undergoes compression. The length region which has not been heated only contributes insignificantly to the pre-stressing force due to the lack of contraction during cooling so that the pre-stressing force can be adjusted by selecting the ratio between the first and second length region in order to also avoid overloading the rivet joint through excessive tensile forces in the rivet joint.
A further aspect of the invention relates to a further hot rivet joint of the type described, in which according to the invention the at least one first component comprises an undercut that cooperates with a plastically deformed region of the shank. A part of the shank of the hot rivet is supported through the undercut so that merely the region between the undercut and the head of the hot rivet contributes to the pre-stressing force. By selecting the position of the undercut the precise adjustment of the pre-stressing force to the desired value is also possible here in order to thus avoid overloading of the rivet joint.
A further aspect of the invention relates to a further hot rivet joint of the type described, in which an opening in the at least one component comprises a widened area. It is also possible through the selection of the width and height of this widened area to adjust the pre-stressing force to a desired value.
A further aspect of the invention relates to a further hot rivet joint of the type described, in which the lower component comprises a thickness reduction on a surface facing away from the shank of the rivet. A targeted adjustment of the pre-stressing force can likewise be achieved through the selection of the size and height of this thickness reduction.
A further aspect of the invention relates to a further hot rivet joint of the type described, in which the lower side of the head is designed in an umbrella shape so that the head contacts the component only in an outer region. In this way the ratio of the inner diameter of the contact surface between the head and component is enlarged and the pre-stressing force is thus indirectly influenced.